For example, a ventilation hole for adjusting an internal pressure is provided to the housing of an ECU (Electronic Control Unit) in an automobile in order to prevent the internal pressure from rising excessively. It is normal for such a ventilation hole to have a measure to prevent the entry of foreign matter, such as dust and water droplets, into the interior of the housing.
For instance, a housing in which a ventilation filter provided with a reinforcing member is attached directly to the ventilation hole is disclosed in JP 2001-168543A. A housing in which a ventilation filter part formed by fixing a ventilation filter to a support body is fit in the ventilation hole is disclosed in Japanese Patent No. 3219700.
In the former case, the ventilation filter is attached to the ventilation hole of the housing by means of heat welding or with the use of an adhesive. However, because the ventilation filter can be damaged at the time of attachment or attached insufficiently, an inspection to confirm the reliability (mainly, the water resistance) is conducted after the attachment. The inspection, however, has to be conducted on large housings as a whole and there is a disadvantage that the inspection apparatus becomes larger. Moreover, in the event of production of an inferior article that failed the inspection, such an article has to be discarded with the whole housing, which is quite wasteful.
In the latter case, because the inspection can be conducted at a stage where a ventilation filter part is formed by fixing the ventilation filter to the support body made of resin, the inspection itself is easy. However, in a case where a method for fitting the ventilation filter part in the housing is adopted, it is essential to devise a configuration such that improves the sealing performance or a configuration such that prevents the ventilation filter part from falling off from the housing. One of the options is to make the ventilation filter part and the housing into one piece by means of heat welding or ultrasonic welding. However, the ventilation filter possibly may be damaged during the application of heat welding or ultrasonic welding.